1. Field of the Invention
The present invention relates to a tertiary amine compound, and an organic semiconductor device and organic electroluminescence device using the compound.
2. Description of Related Art
Organic semiconductor devices typically have a gate electrode, an insulating layer stacked on/above the gate electrode, a source electrode and a drain electrode formed on/above the insulating layer, and a semiconductor layer of an organic compound interposed between the source electrode and drain electrode. The semiconductor layer is formed by the vapor deposition method, application method, drop encapsulation method, vacuum encapsulation method or the like. Organic semiconductor materials suited for respective film forming methods and excellent in current voltage efficiency and length of life are under investigation. Owing to ease of the formation of a semiconductor layer, organic semiconductor devices have advantages such as low cost and mass productivity in a short time.
Such organic semiconductor devices using an organic compound and available at a lost cost can be classified into three groups, that is, low molecule type, polymer type and liquid crystal type.
First, as a polymer type, Appl. Phys. Lett., 62, 1794(1993) describes that organic semiconductor devices using polythiophene, polypyrrole and the like are described. These polymer types are excellent in mass productivity because semiconductor layer can be formed by the application method. In the polymer type organic semiconductor device, however, a polymer is used for the formation of a semiconductor layer between a source electrode and a drain electrode. The polymer has a short life and has higher electrical resistance than a low molecule.
Appl. Phys. Lett., 63, 1372(1993) describes that polythiophene is used frequently as a semiconductor layer in the polymer type. Polythiophene is sparingly soluble in a solution and in addition, owing to heating at high temperature while using a solution of a strong acid such as hydrochloric acid, it tends to cause corrosion of electrodes or deterioration of device performance. It is therefore inferior in mass productivity and device reliability.
Secondly, as a low molecule type, an organic semiconductor device using pentacene is under investigation. It has, however, been generally pointed out as a problem that in this device, an excess voltage must be applied to a gate electrode because a current running between a source electrode and a drain electrode is inevitably small, which results in a drastic increase in a consumed power and in addition, tends to cause dielectric breakdown of an organic film. It burdens an external IC and in addition, makes circuit design difficult, which leads to a cost increase of the IC and deterioration in mass productivity. Also from the viewpoint of performance, the device becomes unstable and has reduced reliability. As a further problem which is expected to occur, the external IC will require a high level and complex circuit design in order to overcome the excessive current flow.
Moreover, pentacene is a low molecular weight compound so that when it is crystallized after vapor deposition, a crystallized portion may presumably become a nucleus of dielectric breakdown. A deposited film of pentacene has many pores so that a uniform film cannot be formed. The semiconductor layer formed using it has a low strength, which lowers the reliability of the device.
As described above, low molecular weight compounds (such as pentacene) used so far for organic semiconductor devices have a problem that a current hysteresis relative to a drive voltage is large. They also have a problem in time-dependent stability, and reliability against impact.
Thirdly, as the liquid crystal type, Appl. Phys. Lett., 73, 1595(1998) describes that organic semiconductors are manufactured by aligning smectic liquid crystals or discotic liquid crystals with an alignment layer formed by an alignment film.
Smectic liquid crystals are rod-like molecules so that they lack in alignment stability and in turn reliability. In addition, liquid crystals are insulators and have high electrical resistance so that the application of a voltage to such semiconductors does not cause smooth current flow, which results in poor switching performance. This increases a load to an external IC and at the same time, may destroy the circuit by much heat generated by high electrical resistance of the materials. As a result, the resulting semiconductor devices have poor mass productivity and reliability.
Many heterocyclic compounds such as thiophene and pyrrole to be ordinarily used for liquid-crystal organic semiconductor devices have a chemical structure not permitting easy packing, have high electrical resistance and lack in durability.
Discotic liquid crystals are disc-shaped molecules. Their molecules pack in the form of columns but difficulty in conjugation results in deterioration in performance related to electrical conduction performance, response and stability.
Such liquid crystals used for liquid-crystal type organic semiconductor devices tend to become nematic by a temperature increase at the starting time of operation so that the packing effect cannot be exhibited fully. Even in smectic liquid crystals, conduction in the direction of their main chain can only be used. Since they are low molecular weight liquid crystals, the conduction mechanism in the main chain cannot be used, resulting in deterioration of the conduction performance of the liquid crystal type organic semiconductor device and conduction performance by the electric field effect.
Most of liquid crystal compounds existing at present are ion conductive type and their response time is slow. Transfer of ions by themselves and accumulation on an electrode on one side leads to deterioration of the device performance. There is accordingly a demand for low-molecular weight organic compounds with which a semiconductor layer can be formed by vapor deposition or injection while making use of the packing effect of them as low molecular weight compounds and have good packing property.